Although there is a need for a randomized trial to address the issue of timing of surgery in infantile ET, APAET, and ANAET, prior to designing such a trial, high-quality preliminary data are needed. We propose a multi-center observational study to 1) determine the duration of misalignment in infantile ET, ANAET, and APAET at study enrollment, 2) to prospectively establish the proportion of patients with angle instability in infantile ET, ANAET, and APAET, and 3) to determine recruitment potential for a randomized trial. These data will be crucial for sample size calculations for the eventual randomized trial, and will help further define the clinical characteristics of these conditions.